The 32-year-old, who was most recently with Grimsby, has joined up with Neal Ardley’s squad as the Magpies moved quickly to replace Kane Hemmings, who left for Dundee on Thursday.
Thomas spent one season at Blundell Park, scoring 11 times in League Two, including one against Notts last December.
And the striker is looking forward to appearing in front of the Meadow Lane faithful.
“There’s a good fanbase here,” said Thomas. “I know that from playing here before.
“It’s always been a really good atmosphere and that’s one of the reasons I wanted to come here.
“This is a massive club and one that should be playing in a higher division so coming here and helping the side to be successful is something that I was eager to do despite dropping down a league.
“I’m looking forward to playing here, scoring a lot of goals and getting the crowd going.”
The striker, who’ll wear number 7, has a host of clubs on his CV, including Birmingham City, Bournemouth, Cheltenham and Oxford.
He made his professional debut in 2008 while at Dagenham and Redbridge and has made over 300 league appearances since.